This invention relates to well cleaning equipment and more specifically, apparatus and method for cleaning out the inside of a liner or casing in an oil or gas well.
It is common practice after drilling a borehole for the purpose of oil extraction, to line the borehole with a well casing and a liner. After installation of the liner, it is generally necessary to clean out the inside thereof in order to wash away any debris or other contaminants.
Various types of cleaning apparatus are known and available. One such type of cleaning apparatus is generically referred to as a casing scraper. This type of tool typically incorporates steel casing scraper blades that scrape the inside of the casing or tubing in the well. Scraper blades are particularly suitable for removing relatively large particles or debris from the surface of the casing or liner. A considerable amount of debris found within the well bore and on the surface of the casing or liner comprises of rust particles and/or metal chips or scrapings originating from equipment used in the well and the casing or liner itself.
Usually, the scraper blades are biased in an outward or radial direction by springs which are designed to maintain the blades in firm contact with the casing wall or other tubing in the well. In the present invention, it is recognised that while this is desirable for the purposes of cleaning the casing and removing debris therefrom, there are other times when the pressure of the casing blades against the tubing or casing is disadvantageous. For example, when a casing scraper is removed from the well, the outwardly biased scraper blades can dislodge further debris causing same to become loose in the circulation fluid and negate the effect of the cleaning work that has already been performed.
Similar difficulties can be encountered with other types of well clean-up tools, including brushes, circulation tools and the like.
An object of the present invention is to obviate or at least mitigate the disadvantage described above and, more particularly, the disadvantage of debris having been removed from the casing wall or liner becoming loose in the circulation fluid, thereby remaining in the well.
In our co-pending British Patent Application Number 9806274.8, there is described apparatus for catching such debris and this is one proposed method and apparatus for dealing with the aforementioned problem. The present invention provides an alternative solution in the form of apparatus and method for collecting loose debris and particles in a well casing or liner. The present invention also provides apparatus which can remove ferrous materials suspended in viscous fluid within a well.
According to the present invention, there is provided apparatus for collecting loose debris or particles in a well casing or liner, the apparatus comprising a body having or supporting one or more magnets.
The apparatus may be a casing scraper having scraper blades, wherein the scraper blades are magnetic.
The apparatus may alternatively be a catcher for catching loose debris particularly during the extraction of the catcher from the well.
The body is preferably adapted for attachment to a work string.
Typically, the magnets are permanent magnets.
The apparatus may comprise a magnetic sub.
In a preferred embodiment the apparatus is comprised of an upper and lower stabiliser wherein a magnetic sub is located between the stabilisers.
The apparatus may also comprise a protective sleeve, positioned over the magnets which preferably can rotate relative to the upper and lower stabilisers. Typically the protective sleeve is made of stainless steel.
The apparatus may be changeable between an inactivated mode wherein the magnetic field which attracts loose debris or particles is off, and an activated mode where the magnetic field is on.
In one embodiment the apparatus comprises a split sleeve having a first and second row of magnets.
Preferably the magnets are selectively activated or deactivated by virtue of moving one of the first or second row of magnets relative to the other of the first or second row of magnets.
According to a second aspect of the present invention, there is a method of trapping or retaining debris or particles in a well casing or liner, the method comprising the steps of:
a) running a magnetic tool or sub in the liner or casing with the magnets inactivated;
b) activating the magnetic tool to create a magnetic force to attract and retain said debris or particles; and;
c) removing the magnetic tool or sub from the well in order to remove the debris or particles.
Preferably, the magnetic tool is located below a well clean-up tool in a work string. The well clean-up tool may be a casing scraper, brushing tool or the like.
Alternatively, the well clean-up tool may comprise a magnetised portion or area, suitably below the cleaning members located on the same tool. The cleaning members may, for example, be casing scrapers, brushes or the like.